Fracking-Linked Earthquakes May Strike Far from Wells

Below:

Next story in Science

ANCHORAGE, Alaska — Fracking may cause earthquakes much farther
from the sites of its wastewater wells than previously thought,
researchers said here Friday (May 2) at the annual meeting of the
Seismological Society of America.

In central Oklahoma, a cluster of four high-volume
wastewater injection wells triggered quakes up to 30 miles
(about 50 kilometers) away, said lead study author Katie Keranen,
a geophysicist at Cornell University in New York. The earthquakes
have since spread farther outward, as fluids migrate farther from
the massive injection wells, she said.

"These are some of the biggest wells in the state," Keranen said.
"The pressure is high enough from the injected fluids to trigger
earthquakes."

Scientists here noted the vast majority of injection wells
haven't triggered any quakes, and the link between earthquakes
and fracking or wastewater injection is not conclusive. However,
there are now more earthquakes in the United States than before
the fracking boom began. Between 1967 through 2000, there were an
average of 21 earthquakes yearly above magnitude 3.0. That rate
shot up to an average of 300 earthquakes yearly after 2010.
[ See Photos of Earthquakes' Paths of Destructions ]

Keranen's new findings were among several studies presented here
this week that draw a strong connection between
fracking practices and earthquakes. Many geoscientists
suspect America's recent sharp increase in earthquakes results
from the growth in fracking. Plotted on a U.S. map, earthquakes
since 2009 cluster near oil and gas operations in states such as
Oklahoma, Ohio, Arkansas and Texas, as well as the usual quake
hot zones in the seismically active Western states.

"It looks like the Earth has a case of the chickenpox," said
Justin Rubinstein, a geophysicist with the U.S. Geological Survey
(USGS) in Menlo Park, Calif.

Fracking is a method of extracting oil and gas from the ground by
fracturing and cracking — or fracking
— rocks. The technique involves forcing millions of gallons of
water laced with chemicals and sand into underground rock to free
trapped oil and gas. After the fracking is finished, the
contaminated wastewater is pumped out and injected back into the
ground, disposed of in wells that are typically much deeper than
the oil and gas reservoirs.

The injected fluid can lubricate buried fault lines and increase
"pore pressure" on a fault's surface, making it easier for a
fault to slip and cause an earthquake.

"Even though only a small fraction of injection wells do induce
damaging earthquakes, there are so many injection operations that
these operations have materially contributed to the seismic
hazard in the U.S.," said Art McGarr, also a geophysicist with
the USGS in Menlo Park. "In states like Oklahoma, where
wastewater continues to be injected, I think it's highly likely
we will continue to see larger earthquakes there."

In Oklahoma, where a magnitude-5.7 earthquake damaged houses in
2011, the earthquake rate now seems to exceed that of California,
once the size of each state is taken into account, said Keranen's
study co-author Geoff Abers, a seismologist at the Lamont-Doherty
Earth Observatory in New York.

Evaluating risk

Because of the recent jump in
earthquakes, and their significant size, the USGS plans to
estimate the national shaking risk from "induced seismicity" for
the first time, Rubinstein said. Induced seismicity refers to any
man-made earthquake, including fracking, wastewater injection and
geothermal plants. [ 50
Amazing Facts About Planet Earth ]

"We've never done this before," Rubinstein said. But "these
earthquakes of larger magnitude really demonstrate that [induced
earthquakes] are a significant hazard."

The new map will help illustrate something that people who live
near wastewater injection wells already know: these shallow,
triggered earthquakes are felt more widely and may cause more
damage than natural earthquakes.

A natural earthquake can strike at any depth, but typically hit
at an average depth of about 6 miles (10 km) in the continental
crust, said Gail Atkinson, a seismologist at Western University
in Ontario, Canada. In contrast, induced seismicity events are
usually 1 to 2 miles (2 to 3 km) deep. "The close distance means
that ground motion can be quite strong," Atkinson said.

The rising number of man-made earthquakes may pose a risk to
critical infrastructure such as dams and nuclear power plants,
according to a study presented by Atkinson on Thursday (May 1).
But the danger is still unknown.

"Our experience comes from earthquakes that are much deeper," she
said. "There is quite an absence of a regulatory framework in
terms of how to evaluate what the hazard is and who is
responsible for assessing and responding to it," Atkinson said.